From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754102Ab3HBKTk (ORCPT ); Fri, 2 Aug 2013 06:19:40 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:37756 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752837Ab3HBKTi (ORCPT ); Fri, 2 Aug 2013 06:19:38 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Michael S. Tsirkin" , "David S. Miller" , Wolfram Gloger , Ben Hutchings Subject: [ 37/39] virtio: support unlocked queue poll Date: Fri, 2 Aug 2013 18:18:47 +0800 Message-Id: <20130802101502.037923320@linuxfoundation.org> X-Mailer: git-send-email 1.8.3.4.841.g1a3f60e In-Reply-To: <20130802101456.800497005@linuxfoundation.org> References: <20130802101456.800497005@linuxfoundation.org> User-Agent: quilt/0.60-5.1.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michael S. Tsirkin commit cc229884d3f77ec3b1240e467e0236c3e0647c0c upstream. This adds a way to check ring empty state after enable_cb outside any locks. Will be used by virtio_net. Note: there's room for more optimization: caller is likely to have a memory barrier already, which means we might be able to get rid of a barrier here. Deferring this optimization until we do some benchmarking. Signed-off-by: Michael S. Tsirkin Signed-off-by: David S. Miller [wg: Backported to 3.2] Signed-off-by: Wolfram Gloger [bwh: Backported to 3.4: adjust context] Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- --- drivers/virtio/virtio_ring.c | 54 ++++++++++++++++++++++++++++++++++--------- include/linux/virtio.h | 4 +++ 2 files changed, 47 insertions(+), 11 deletions(-) --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -498,16 +498,18 @@ EXPORT_SYMBOL_GPL(virtqueue_disable_cb); * virtqueue_enable_cb - restart callbacks after disable_cb. * @vq: the struct virtqueue we're talking about. * - * This re-enables callbacks; it returns "false" if there are pending - * buffers in the queue, to detect a possible race between the driver - * checking for more work, and enabling callbacks. + * This re-enables callbacks; it returns current queue state + * in an opaque unsigned value. This value should be later tested by + * virtqueue_poll, to detect a possible race between the driver checking for + * more work, and enabling callbacks. * * Caller must ensure we don't call this with other virtqueue * operations at the same time (except where noted). */ -bool virtqueue_enable_cb(struct virtqueue *_vq) +unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); + u16 last_used_idx; START_USE(vq); @@ -517,15 +519,45 @@ bool virtqueue_enable_cb(struct virtqueu * either clear the flags bit or point the event index at the next * entry. Always do both to keep code simple. */ vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; - vring_used_event(&vq->vring) = vq->last_used_idx; + vring_used_event(&vq->vring) = last_used_idx = vq->last_used_idx; + END_USE(vq); + return last_used_idx; +} +EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare); + +/** + * virtqueue_poll - query pending used buffers + * @vq: the struct virtqueue we're talking about. + * @last_used_idx: virtqueue state (from call to virtqueue_enable_cb_prepare). + * + * Returns "true" if there are pending used buffers in the queue. + * + * This does not need to be serialized. + */ +bool virtqueue_poll(struct virtqueue *_vq, unsigned last_used_idx) +{ + struct vring_virtqueue *vq = to_vvq(_vq); + virtio_mb(vq); - if (unlikely(more_used(vq))) { - END_USE(vq); - return false; - } + return (u16)last_used_idx != vq->vring.used->idx; +} +EXPORT_SYMBOL_GPL(virtqueue_poll); - END_USE(vq); - return true; +/** + * virtqueue_enable_cb - restart callbacks after disable_cb. + * @vq: the struct virtqueue we're talking about. + * + * This re-enables callbacks; it returns "false" if there are pending + * buffers in the queue, to detect a possible race between the driver + * checking for more work, and enabling callbacks. + * + * Caller must ensure we don't call this with other virtqueue + * operations at the same time (except where noted). + */ +bool virtqueue_enable_cb(struct virtqueue *_vq) +{ + unsigned last_used_idx = virtqueue_enable_cb_prepare(_vq); + return !virtqueue_poll(_vq, last_used_idx); } EXPORT_SYMBOL_GPL(virtqueue_enable_cb); --- a/include/linux/virtio.h +++ b/include/linux/virtio.h @@ -44,6 +44,10 @@ void virtqueue_disable_cb(struct virtque bool virtqueue_enable_cb(struct virtqueue *vq); +unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq); + +bool virtqueue_poll(struct virtqueue *vq, unsigned); + bool virtqueue_enable_cb_delayed(struct virtqueue *vq); void *virtqueue_detach_unused_buf(struct virtqueue *vq);